Wide-Board Table Top with no Warping

Can it be done? Maybe. February 26, 2005

I have come across some wide ash and walnut boards. The boards are 4/4 and 16"-18" wide. If I were to use one of these species for a harvest table top, would a few saw kerfs on the backside of these boards, say 1/4"-3/8" deep, be enough to prevent warping of these boards? I would then use wood screws to fasten the table to the apron. Or if I were to use bread board ends, would I still get warping in the mid section of the table? Perhaps another option would be a sliding dovetail joint attached to a hefty cross piece across these boards. To save time, are there any dovetail type components on the market for this application? Any thoughts or observations would be appreciated.

Forum Responses
(Furniture Making Forum)
From contributor P:
All bets are off unless…
1) The MC is real stable.
2) You use a screwed strongback underneath every 12 to 16". Don't forget to elongate the holes for expansion/contraction, along with the apron.
3) You finish it as soon as possible to seal it.
4) You cross your fingers.

The breadboard edge is a nice touch, but if the table does decide to warp, it's going to break the edge boards at the thinnest part, as it shouldn't be glued, either. Why wouldn't you want to saw and joint the edges anyway? You wouldn't see the glue joint if it's done well and you would relieve a lot of the stress from the wood.

From the original questioner:

I was hoping to keep the natural grain pattern of those large boards. I am always impressed when I see a table made of just a few planks (cracks and all). However, after giving it some thought, the odds of failure may not be worth the effort.

From contributor M:
If the table is for you or for a show table, I say go for it. If it is an order for a customer and they are expecting it not to crack or warp, you would be well advised to rip, edge and reglue with opposing grain. 4/4 is just too thin to expect them not to warp over that width, no matter how you finish or attach to table. Whatever you do, make sure to finish all sides and elongate holes for screws for movement.

From contributor Y:
When faced with a situation like this, I always double or triple mill my stock. Assuming you have 4/4 rough, I would joint and plane no more than a 1/16 off each face, just enough to remove most of the fuzz, sticker and let rest in a stable environment (preferably the place where the finished product will eventually reside) for as long as you can wait. A couple of weeks at least. Joint and plane another light pass, let rest again. By now you should have a board approximately 15/16" to 1" thick and much more stable than if you had milled, cut and assembled without resting it first. If you can afford a thinner top, by all means let rest again before taking that final light pass on the jointer and planer before cutting your joinery. It's important to observe how your wood behaves along the way and manipulate it to get the straightest result when milling it. I have done this many times and always have good results unless the wood is badly warped to begin with and I can't straighten it out without crosscutting it into shorter lengths. And of course, seal it as soon as you are done milling.

From contributor S:
I used to take the warp out of 12" wide 4/4 figured maple boards by plunging flutes along the bottom length using a 1" diameter core box bit. I don't remember if that is the right name for the bit. The concave recess weakens the resistance the board exerts when you straighten the board by screwing the apron to it. The deeper you go, the less resistance. Common sense has to take over with the method I described. Extra cross bracing might be needed.

I don't like saw kerfs because of the concentrated stress that the kerf corners bring to the stress relief. The concave profile distributes the stress more evenly.

I agree with your reasons for trying to keep the boards in one piece, at least on the part that shows.

From contributor S:
I liked contributor Y's suggestion on how to keep wide boards from warping. I especially agree on removing the fuzz equally from both sides. I remember reading how the drying process tends to case-harden the outer surface layers of lumber. If you leave some of that hardening stress on one side, you are almost guaranteed a warping problem.

From contributor J:
I would like to know just how the old timers (2 to 3 hundred years ago) built their wide table tops. They still haven't warped ! Must've been some extremely stable trees.

From contributor Y:
I think they air dried their lumber back then, which makes for more stable wood. Probably 2 or 3 years from the time the wood was milled until final usage. Just my guess.

From contributor D:
Tables and things that were built 200-300 years ago and are still around today are the ones that survived. The ones that cracked, warped, split, etc. self destructed or were recycled long ago. Survival of the fittest and all. Reading about old shops (Compleat Cabinetmaker of late 1700's in US) talks about the wood inventory as a major resource of every woodshop. It would be stockpiled for years. Remember, the trees were huge, and mostly in the way of agriculture/development. The material was free for the taking. The best was saved, the rest burned for heat or charcoal. A lot different from today.

From contributor M:
Correct me if I am wrong. But I also believe it had to do with the old growth trees which were more dense and do not migrate nearly as much as the lumber we are all using now.

From contributor D:
You are right. The slow growth really packed in the annual rings and made for a stable plank.